Hall Effect sensors are used in many automobile applications. One application is to use a Hall Effect sensor to measure the timing in ignition systems. Other applications use Hall Effect sensors to detect the position of the crankshaft and camshaft and to monitor engine RPM. The signal generated by these sensors are used to ensure that proper engine timing is maintained.
In electronic ignition systems, Hall Effect sensors are used to ensure that spark plugs ignite a compressed air-fuel mixture within the engine at an optimum position. To do so at least one ferrous target is mounted or integrated into a rotating engine component, such as the crank shaft. As the target approaches the Hall Effect sensor, containing a magnet, the sensor detects the flux field changes and produces an electric signal. The electric signal in turn is processed and used to trigger an ignition box. The electric signal can be a signal that is either 12 volts or ground and depends on the relative position of the target to the sensor. As the ferrous target approaches a sensor the field flux increases through the sensor. At a critical field flux density the sensor switches from 5 volts, the peak, to ground, the low. The minimum distance position represents the moment when the engine is at peak power, such as optimum compression in a combustion chamber. The passing of the target past the sensor creates a pulse with a width. The pulse has a leading edge that transitions from 5 volts to ground and a trailing edge that transitions from ground to 5 volts. The pulse is modified to a 12 volt high and the ignition box triggers the spark plugs as it detects a 0 to 12 volt edge rise in the pulse. The intention is for the spark plugs to ignite when the engine can produce peak power.
FIG. 1 depicts a Hall Effect Pickup incorporated into an engine component 100. Engine component 100 comprises a rotating shaft 111, which is coupled to oscillating piston elements (not shown) in the engine. Coupled to shaft 111 is reluctor 112. Reluctor 112 comprises 8 ferrous blades 113. The position of the blades 113 on Reluctor 112 corresponds to the compression positions of the piston elements. Engine component 100 also comprises a bell distributor housing 114 that partially encompasses shaft 111. A Hall Effect sensor 115 is coupled to the inner wall of housing 114. As the shaft 111 rotates, the blades 113 of reluctor 112 also rotate. As a first blade 113 approaches sensor 115 the sensor 115 detects the increasing flux field strength. The field strength will be at its maximum when the spacing between sensor 115 and blade 113 is at a minimum. At a critical flux field strength, the sensor 115 will trigger and switch from 5 volts to ground. The rotation of blades 113 past sensor 115 decreases the field strength about sensor 115. The field increases once again as a second blade approaches the sensor 115. The rotation of blades 113 means that sensor 115 is producing a signal with a period that will correspond to the time between each blade reaching a minimum separation from the sensor 115. Thus, the frequency of the resulting Hall Effect signal reflects the revolutions per minute of the reluctor 112, and consequently the engine. At low RPMs, the frequency of the Hall Effect signal will be low, and consequently long periods. At high RPMs, the frequency of the Hall Effect signal will be high, and consequently short periods.
In order to have engine peak power the trigger of the Hall Effect signal should occur at the same moment in time as a blade being at a minimum separation from the sensor. However, there is an inherent delay between the position of a blade and the trigger of the Hall Effect signal in time. As a result, the leading edge of a pulse will be off by a time t1 from the moment when the blade 113 is first in detection proximity to the sensor 115 and off by a time t3 from the moment when the blade 113 moves away from the detection proximity of sensor 115. The time t1 should correspond or be equal to time t3. As a result, the triggering edge of the pulse is displaced to a moment that does not correspond to the minimum spacing of the blade 113 to the sensor 115 or the optimum power position of the engine. The time span between the leading edge of the pulse and the moment that the blade moves away from the detection proximity is considered time t2. Thus, the phase of the Hall Effect signal will not accurately represent the position of the blade in time. This can be due to the delay in the Hall Effect sensor detecting the position of a rotating blade and the time it takes for the Hall Effect sensor to process a signal. By the time that the triggering edge of the Hall Effect signal reaches a spark plug the engine is no longer in a position of peak power, such as optimum piston compression. This results in a loss of engine efficiency. When an engine operates at low revolutions per minute the period of a Hall Effect signal is relatively long. As a result, the relationship between degree of displacement from peak power and ignition, i.e. the degree in which the signal and piston are out of phase may only be slight. However, when an engine is operating at high revolutions per minute the period of a Hall Effect signal is much shorter. This means that the degree to which peak power and the signal are out of phase is much more pronounced and significant. As a result, there is a greater loss of efficiency at higher RPMs.
What is needed is a method and device that achieves maximum precision of engine timing. It would be beneficial if such a method could correct the timing of a Hall Effect sensor. It would also be beneficial if the method could be achieved by a circuit that is coupled to the Hall Effect sensor.